How to cover a surface with cells (Biological tissue)
Final:



Overview:

I think the best option would be to use Metaball as a Hair object. 

This method will need a little bit of experimenting as it could highly differ between meshes.



Metaball settings:

In Edit Mode set Resolution as low as possible, it will be better looking while rendering, as preview resolution is always a bit lower. 

Really low Threshold along with high Stiffness will give more defined Mballs. As well as scaling Ellipsoid on Y axis. Higher scaling, more noticeable bumps.



Particle System settings:

Nothing fancy here.

Tweak all settings as you like. In this example I've used ones below.